Consolidated Statements Of Income And Earnings Reinvested In The Business (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
INCOME
Operating Revenues	$ 491,095	$ 552,544	$ 935,283	$ 1,042,791
Operating Expenses:
Purchased Gas	118,270	195,037	210,542	333,697
Property, Franchise and Other Taxes	22,743	22,535	45,887	46,540
Depreciation, Depletion and Amortization	77,912	65,664	152,830	129,918
Impairment of Oil and Gas Producing Properties	177,761	0	177,761	0
Total Operating Expenses	515,675	399,185	811,843	727,748
Operating Income (Loss)	(24,580)	153,359	123,440	315,043
Other Income (Expense):
Other Income (Deductions)	(17,480)	(5,919)	(20,520)	(15,521)
Interest Expense on Long-Term Debt	(25,270)	(25,273)	(50,713)	(50,713)
Other Interest Expense	(1,892)	(1,787)	(3,443)	(2,860)
Income (Loss) Before Income Taxes	(69,222)	120,380	48,764	245,949
Income Tax Expense	36,846	29,785	68,241	52,693
Net Income (Loss) Available for Common Stock	(106,068)	90,595	(19,477)	193,256
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Period	1,320,592	1,172,334	1,272,601	1,098,900
Beginning Retained Earnings Unappropriated And Current Period Net Income	1,214,524	1,262,929	1,253,124	1,292,156
Dividends on Common Stock	(37,654)	(36,678)	(75,304)	(73,342)
Balance at March 31	$ 1,176,870	$ 1,236,657	$ 1,176,870	$ 1,236,657
Earnings Per Common Share, Basic:
Net Income (Loss) Available for Common Stock (in dollars per share)	$ (1.23)	$ 1.05	$ (0.23)	$ 2.24
Earnings Per Common Share, Diluted:
Net Income (Loss) Available for Common Stock (in dollars per share)	$ (1.23)	$ 1.04	$ (0.23)	$ 2.23
Weighted Average Common Shares Outstanding:
Used in Basic Calculation (shares)	86,561,066	86,290,047	86,469,258	86,159,932
Used in Diluted Calculation (shares)	86,561,066	86,767,673	86,469,258	86,738,809
Dividends Per Common Share:
Dividends Declared (in dollars per share)	$ 0.435	$ 0.425	$ 0.870	$ 0.850
Utility and Energy Marketing [Member]
INCOME
Operating Revenues	$ 282,634	$ 357,654	$ 510,660	$ 629,747
Operating Expenses:
Operation and Maintenance	51,725	48,559	94,981	92,475
Exploration and Production and Other [Member]
INCOME
Operating Revenues	156,542	146,467	323,735	310,403
Operating Expenses:
Operation and Maintenance	39,959	40,141	76,652	72,936
Pipeline and Storage and Gathering [Member]
INCOME
Operating Revenues	51,919	48,423	100,888	102,641
Operating Expenses:
Operation and Maintenance	27,305	27,249	53,190	52,182
Guidance for Hedging [Member]
EARNINGS REINVESTED IN THE BUSINESS
Cumulative Effect of Adoption of Authoritative Guidance	0	0	(950)	0
Guidance for Recognition and Measurement of Financial Assets and Liabilities [Member]
EARNINGS REINVESTED IN THE BUSINESS
Cumulative Effect of Adoption of Authoritative Guidance	0	0	0	7,437
Guidance for Reclassification of Stranded Tax Effects [Member]
EARNINGS REINVESTED IN THE BUSINESS
Cumulative Effect of Adoption of Authoritative Guidance	$ 0	$ 10,406	$ 0	$ 10,406